Separation methods for water treatment include a method using heat or phase-change, a method using a filtering membrane, and so on. The method using a filtering membrane has a lot of advantages over the method using heat or phase-change. Among the advantages is the high reliability of water treatment since the water of desired purity can be easily and stably obtained by adjusting the size of the pores of the filtering membrane. Furthermore, since the method using a filtering membrane does not require a heating process, it can be used together with microorganisms which are useful for separation process but vulnerable to heat.
Among the methods using a filtering membrane is a method using a hollow fiber membrane module comprising a bundle of hollow fiber membranes. Typically, a hollow fiber membrane module has been widely used in the field of microfiltration for obtaining axenic water, drinking water, super pure water, and so on. Recently, the application of the hollow fiber membrane module is being extended to wastewater treatment, solid-liquid separation in a septic tank, removal of suspended solid (SS) from industrial wastewater, filtration of river, filtration of industrial water, filtration of swimming pool water, and the like.
The hollow fiber membrane module may be classified into a submerged-type module and a pressurized-type module based on the driving method.
The submerged-type module performs the filtration operation while submerged in a fluid to be treated. Particularly, as the negative pressure is applied to the inside of the hollow fiber membrane, only the fluid exclusive of impurities is allowed to pass through the hollow fiber membrane and enter the inside (lumen) thereof. As a result, the pollutants such as the impurities and sludge contained in the fluid are separated from the filtrate. The submerged-type module is advantageous in that it does not require additional facilities for circulating the fluid, and thus the cost of equipment as well as the operation cost can be reduced. On the other hand, it has a drawback in that the permeate flux obtainable per unit time is limited.
On the contrary, although requiring additional facilities for circulating the fluid, the pressurized-type module pressurizing the fluid from the outside to the inside of the hollow fiber membrane is advantageous in that its permeate flux obtainable per unit time is larger than that of the submerged-type module.
Hereinafter, referring to FIG. 1, a conventional pressurized-type hollow fiber membrane module will be described.
As shown in FIG. 1, a conventional pressurized-type hollow fiber membrane module 10 comprises a case 11 disposed in such a way that its lengthwise direction is perpendicular to a ground G and a hollow fiber membrane (not shown) therein.
The case 11 has the first inlet IL1 for receiving the feed water to be treated, the first outlet OL1 for discharging the filtrate passing through the hollow fiber membrane, the second inlet IL2 for receiving the air for aeration cleaning of the hollow fiber membrane, and the second outlet OL2 for discharging the overflow and/or air out of the case 11.
As shown in FIG. 1, since the first inlet IL1 is formed on the lower part of the case 11 and the first outlet OL1 is formed on the upper part thereof, the conventional pressurized-type hollow fiber membrane module requires a pump P1 as a means for providing a driving force against the gravity (i.e., a means for pressurizing the fluid to be treated).
Consequently, due to such pump P1, there is a limit in reducing the energy consumption of the conventional pressurized-type hollow fiber membrane module 10.